MONTREAL — If you were looking for a place to explore how the world has changed in the past half-century, you could do worse than venture here and contemplate the glory that was Expo 67, perhaps the greatest World’s Fair of the 20th century and certainly the most popular.

The fair, which opened 50 years ago Thursday, carried the slogan “Man and His World.” No one would ever use “man” as a synonym for “humanity” today. Visitors wandered easily through its gates and into the pavilions of the five dozen nations that participated and the scores of companies that contributed exhibits. Security concerns would make that inconceivable today. The fair created, or reflected, a burst of Canadian unity. Within months that unity would be shattered and Quebec separatism would gain new urgency and passion.

“It was a special year — a vintage year — and it is probable that we will not see its like again,” the Canadian historian Pierre Berton wrote of 1967, when Canada celebrated the centenary of its confederation. With a generational turnover in Canadian leadership looming, government commissions here dealt with sensitive issues of gender and language. The country was convulsed in debate over social issues and the presence of American draft dodgers.

Even so, Mr. Berton concluded, 1967 “was a year in which most Canadians felt good about themselves and their country.”

A principal reason was Expo, which attracted more than 50 million people and was described by the respected Canadian writer Peter C. Newman as “the greatest thing we have ever done as a nation.”

Here in Montreal, visitors could see a film at the Canadian Pacific pavilion, taste one of the 60 beers at the Brewers pavilion, linger in a garden provided by the Principality of Monaco, or sample reindeer or moose steak in the Scandinavian pavilion. South Korea displayed a 16th-century ironclad ship, Cuba served daiquiris. Togo offered its vision of “a smiling land of happy people.”

Actually Canada was mostly a smiling land of happy people, though French President Charles de Gaulle added an arch political moment when, from a balcony of Montreal’s city hall, he issued a battle cry that echoes still: “Vive le Québec libre,” which means “long live a free Quebec” — and which set many Francophone hearts ablaze. Neither Montreal nor Canada would be the same again.

That was probably the most significant legacy of 1967, but it was not alone. Coming roughly midway between the country’s new maple-leaf flag and its official adoption of “O Canada” as the national anthem, Expo brought the world to Canada and took Canada to the world. Within a year, the charismatic Pierre Elliott Trudeau — elegant, intellectual, flawlessly bilingual — would become prime minister and a symbol of the country’s new mod visage.

Little of that 1967 excitement remains, though the ascension of Mr. Trudeau’s son, Justin, to Canadian leadership last year added a fresh layer of stardust to Canadian politics. But the Canadian landscape retains another remnant of Expo and the experimental air that surrounded it. It is called Habitat 67, and it still sits across a spit of water from Montreal’s Old City.

The brainchild of architect Moshe Safdie, who conceived of it as a student project, Habitat consists of 354 modules, each weighing 70 tons and lifted like Legos onto the structure by specially built cranes and outfitted with pre-fab kitchens and bathrooms. If Habitat were a painting, the canvas would belong to Georges Braque or Pablo Picasso, masters of Cubism the way Mr. Safdie was the master of concrete cubes.

“This is one of the last symbols of Expo 67,” said Robert Stephen Lefebvre, a retired lawyer who now sells units in Habitat. “But it’s much more than that. This is an amazing place, found in architecture books around the world.”

Indeed, Habitat endures and today is a much-coveted address, with units, fitted with solariums and terraces, now sometimes exceeding $1 million. Many of the once-modern conveniences of 1967 have been updated, and many residents have added features. “People have demonstrated in their adaptations how versatile the modules have been,” Mr. Safdie said in an interview.

As symbols of the period go, few are more enduring than the Montreal masterpiece produced by Mr. Safdie, who is also known for his design of the Yad Vashem museum in Jerusalem and the headquarters of the United States Institute of Peace in Washington.

“Habitat was a magic moment in architecture just as Expo was in culture,” says Franklin Toker, a Montreal native who is an art and architectural historian at the University of Pittsburgh. “Habitat and Expo were the product of technological advances, the harmony of the races — and a slight dig at the Americans because Expo was so much more successful than the New York World’s Fair in New York.”

But almost everything else about Expo is part of a fast-vanishing past.

Two of the more colorful visitors were the Shah of Iran and the emperor of Ethiopia, two titles that do not exist today. Expo was the stage set for performances of “The Ed Sullivan Show” and Petula Clark, names unknown to half of Canadians, who have a median age of about 40, and who do not represent the “Canadian content” that became de rigueur a year after Expo. The official handbook lists a full page of souvenirs from the Soviet Union, which has disappeared, nor is it still certain that, as the advertisement put it, “a garment of Russian Sable is one gift guaranteed to make a woman happy.” Even the baseball team that was named for Expo 67 has vanished. Now the team of Andre Dawson and Gary Carter is the Washington Nationals.

As the fair closed — and with it a shimmering moment in the history of Canada — Prime Minister Lester B. Pearson identified the legacy of Expo, and of the year 1967 in Canada:

“Expo’s lasting impact is: That the genius and fate of man know no boundaries but are universal; that the future peace and well-being of the world community of men depend on achieving the kind of unity of purpose within the great diversity of national effort that has been achieved here at this greatest of all Canada’s Centennial achievements.”

For the past 50 years Canada and its partners and friends around the world have sought to recapture that sense of purpose. We could all use a little bit of it now, a half-century on.

David Shribman, a Pulitzer Prize winner in journalism, is executive editor of the Pittsburgh Post-Gazette.